nycti-, nyct-, nycto-, nyc- +

(Greek: night; a relationship to darkness, dark)

By night; nightly.
An old medical term that refers to the eruption that affects the skin on the arms, hands, and thighs only at night.
geonyctitropism (s) (noun), geonyctitropisms (pl)
Orientation movements in plants during darkness as they respond to gravity.
A night and a day; a period of twenty-four hours.

This word is frequently spelled "nycthemeron". It was written as such because in classical times a new day started at sunset, a rule continued in some religions today. Although nychthemeron is generally unknown, it is still used by some people, as well as its adjective, "nychthemeral".

Those scientists who study the ways in which the body's physiological activity varies hour by hour, as in sleep research, make a distinction between nychthemeral and the more common Latin-derived circadian which comes from circa, "round, around" + dies, "day".

Circadian refers to daily cycles that are driven by an internal body clock, while nychthemeral rhythms are the result of the external environment.

1. Night blindness; failure or imperfection of vision at night or in a dim light.

Smoking tobacco may impair the ability to see at night. Hypoxia associated with being above sea level in an aircraft will also decrease night vision.

2. The inability to see well under scotopic (dark) conditions, due to faulty rod function.

The “rod” used here refers to any of the photoreceptor cells of the retina serving scotopic vision. “Scotopic vision” designates the dark-adapted state of vision, in which color perception is replaced by shades of black and white. It is served by the rod photorecptors.
3. A condition of the eyes in which the person can see well during the day, in a strong light, or on bright days, but see poorly at night, in a faint light, or on dull or dark days; night blindness; day sight.
4. The opposite of nyctalopia is hermeralopia, or day blindness.

Reduction, or dimness, of vision at night without visible eye changes.
Flowering only during the night.
An elective mutism indicating the loss of one's voice during the night.
Someone who hunts by night.
Nocturnal; or pertaining to night, especially to a night-time period of animal activity.
nycthemeral, nycterohemeral nyctohemeral
Of or relating to the alternation of night and day, particularly a single night followed by day; a full period of night and day.
A reference to flowers that open at night and close during the day; nygtigamy.
A genus of bioluminescent marine organisms that, when grouped in large numbers, make the seas phosphorescent.
nyctinasty, nytinastic, nyctinastism
1. The movements of flowers or leaves, caused by a regular cycle of changes in light and temperature.
2. Orientation movements of plants during the night.

Nastic movements of plant organs in response to the changes in light and temperature that occur between day and night (and vice versa). Examples are the opening and closing of many flowers and the folding together of the leaflets of clover and other plants at night.

nyctipelagic (adjective) (not comparable)
Pertaining to living things that migrate or rise into the upper surface of water only at night: Bathypelagic organisms, such as pteropods, heteropods, and various crustaceans and siphonophores, are all examples of nyctipelagic organisms that sink from the higher levels to the lower levels of the sea during the day.

Bathypelagic refers to creatures that live in deep water below the level of light penetration, between 1,000 meters and 4,000 meters deep.

Other related "dark; shadow, shade; black" units: lygo-; melan-; nigri-; nocti-; scoto-; skio-; umbra-.

Another related "night" unit: nocti-.